1. Field of the Invention
This invention relates generally to storage, separation and analysis of ions according to mass-to-charge ratios of charged particles and charged particles derived from atoms, molecules, particles, sub-atomic particles and ions. More specifically, the present invention is a combination of two or more trapping regions in a single device that enables a user to obtain increased sensitivity without suffering the effects of high space-charge, and increased resolution for greater analytic capability.
2. Description of Related Art
Mass spectrometry continues to be an important method for identifying and quantifying chemical elements and compounds in a wide variety of samples. Mass spectrometry is also among the most widely used analytical techniques. The combination of high sensitivity, high chemical specificity, and speed make it a method of choice for many applications.
Mass spectrometers are used in such areas as proteomics research, clinical analysis, protein sequencing, planetary science, geology, identification and structural determination of organic molecules, drug discovery, surface characterization, forensics, study of chemical reactions, elemental analysis, manufacturing, security screening, air monitoring, etc. High sensitivity and selectivity of mass spectrometry are especially useful in threat detection systems (e.g. chemical and biological agents, explosives) forensic investigations, environmental on-site monitoring, and illicit drug detection/identification applications, among many others.
Many mass spectrometers on the market use ion traps for mass analysis. In ion traps, ions are contained and analyzed using radiofrequency electric fields. Primarily quadrupolar fields are used, but numerous variations exist in which other fields are used to manipulate the ions. For instance, small dipole or octupole fields can be used to increase performance. Monopoles, dipoles or direct-current biases can be used for ion ejection. Ions or charged particles can be trapped for long periods of time and used for various other experiments. The numerous variations have led to many specialized applications and experiments that cannot be done any other way. In addition, efforts at producing miniaturized and portable mass spectrometers are based primarily on ion trap mass analyzers.
Several variations of ion trap mass spectrometers have been developed for analyzing ions. These devices include quadrupole configurations, as well as Paul, dynamic Penning, and dynamic Kingdon traps. In all of these devices, ions are collected and held in a trap by an oscillating electric field. Changes in the properties of the oscillating electric field, such as amplitude, frequency, superposition of an AC or DC field and other methods can be used to cause the ions to be selectively ejected from the trap to a detector according to the mass-to-charge ratios of the ions.
Of particular relevance to the present invention is the development of a “virtual” ion trap that is taught in U.S. Pat. No. 7,227,138. The '138 patent teaches the use of electric focusing fields instead of machined metal electrodes that normally surround the trapping region. In the virtual ion trap electric focusing fields are generated from electrodes disposed on generally planar, parallel and opposing surfaces such as plates. The term “virtual” thus applies to the fact that the confining walls of electrodes are replaced with the “virtual” walls created by the electric focusing fields. The electrodes are disposed on the two opposing plates using photolithography techniques that enable much higher tolerances to be met than existing machining techniques.
The '138 patent also teaches that electrodes used to create a trapping region in conventional ion traps also created substantial barriers, by themselves, to the flow of ions, photons, electrons, particles, and atomic or molecular gases into and emissions out of the ion traps.
Several important features are described in the '138 patent about the embodiments of the virtual ion trap. First, some solid physical electrode surfaces of linear RF quadrupoles and other prior art ion traps are eliminated in favor of virtual electrodes. The virtual electrodes are formed by arranging a series of one or more electrodes on the opposing plates that generate constant potential surfaces similar to the solid physical surfaces that the electrodes replace.
Second, the opposing plates or faces as they are sometimes called are aligned so as to be mirror images of each other.
Third, the opposing faces are substantially parallel to each other.
Fourth, the opposing faces are substantially planar. However, it is noted that the opposing faces may be modified to include some arcuate features. However, optimum results will be maintained by making the opposing faces generally symmetrical with respect to any arcuate features that they may have to thereby make it easier to create a desired trapping region.
FIG. 1 is provided as an illustration of an embodiment of the virtual ion trap 10 described in the '138 patent. The inside and opposing faces 12 have an oscillating electrical field 14 applied thereto. The outside faces 16 have a common potential applied that is a common ground in this case.
It is observed that some of the systems described above, such as the virtual ion trap, are capable of generating multiple trapping regions. However, none of the systems above has been used to create more than one type or shape of trapping region. Accordingly, it would be an advantage over the prior art to provide a mass analyzer that is capable of generating at least two different types of trapping regions so that the advantages of each can be exploited simultaneously in a single device.